The following Frequently Asked Questions (FAQ) focus on databases and
VisualAge for Smalltalk:
What databases are supported by VisualAge? |
| VisualAge for Smalltalk supports a wide variety of database systems
including: The DB2 family. On the client: DB2/2 for OS/2, DB2/6000 for AIX, and
on Windows using CAE client support. Through connectivity services of DDCS,
VisualAge for Smalltalk can access the DB2 family (including DB2 and SQL/DS and
access to the AS/400). ORACLE ODBC (with industry standard drivers such as
Sybase, SQL Server, Informix) IBM intends to respond to additional customer
needs for native support for other databases. |
|
Is ODBC fully supported by VisualAge? |
| Yes, all the capabilities in the ODBC standard are supported starting with
VA 3.0. |
|
Does VA support ODBMSs? |
Versant Versant is an IBM Object Connection partner. They provide
their Argos development environment and OODBMS (Release 4) which can be used
with IBM Smalltalk and IBM's VisualAge for Smalltalk. Argos is a modeling tool
and is described in Section XVII. Versant's OODBMS is a leading object database
management system for multi-user, distributed applications. Versant can be
reached at 1-800-VERSANT.
Gemstone Gemstone Systems is also an
IBM Object Connection partner. They provide their Gemstone Object Application
Server for VisualAge which allows VisualAge applications to take advantage of
GemStone's three-tier application partitioning capabilities for
business-critical enterprise-wide deployment. Gemstone can be reached at
1-800-243-9369.
Tensegrity Polymorphic Software, Inc., also
and Object Connection partner, has announced plans to make their Tensegrity
OODBMS available for IBM Smalltalk. Polymorphic can be reached at 415-592-6301.
ODI IBM is working with ODI to enable their ObjectStore OODBMS
to IBM Smalltalk. This support is currently planned for VisualAge for Smalltalk
V4.0. |
|
Explain the use of multirow query settings. |
| Maximum number of rows to fetch - used with a one-time query to limit the
rows returned Enable packeting - for DB2/2, quick forms, and containers, return
up to the number of rows that will fit on the display area; get more rows as
needed to satisfy the user actions (e.g. scrolling) Enable blocked fetches - for
ODBC, get up to the number of rows that you specify in the Blocked fetch size
for each request. |
|
What would cause my database query to show no fields? |
One of two things, either
(1) the database is not set up
and/or connected to properly.
See pp.12 - 18 of the VA User's Guide for
connecting to a DB. If you're using DB2, make sure you also bind to the DB (pp.
421-3). Use your DBMS tools to set up the DB schema
or
(2) the query is not set up properly.
The
DB query part has a settings popup. In the resulting dialog, define your query
- see pp. 19 - 28 of the VA User's Guide. |
|
Can I connect to two data sources concurrently? |
| If you have VisualAge 3.0 or later, then you can create multiple connection
specs, and connect to all of them simultaneously. The number of connections
vary by database vendors. |
|
Can I disable the AbtError message from appearing from queries so I can
handle them myself? |
What you can do is the following:
- extend the AbtDatabasePart class
into your application
- add an #initialize instance method
setting the (individual) errorBlock to whatever you want
- just
make sure you have "super initialize" as the first statement
|
|
Can I have more than one connection to DB2 using ODBC? |
| You can connect to DB2 via ODBC as many times as the driver permits,
however the DB2 driver that we ship with the ODBC support only supports 1
connect at a time. The DB2 CLI driver can be used as an ODBC driver, but this
driver is not fully ODBC compliant, and you will have problems using our SQL
editor. |
|
How do I asynchronously access a DB2 database? |
The Database tab of the VisualAge preferences notebook contains a check box
'Thread all database calls'. This feature is currently operational on OS/2
only. Setting this option causes external database calls to execute on a
separate Smalltalk thread.
To view the preferences page, go to the
VisualAge Organizer view, select Options->Preferences. Any change
to this option will become effective when you click 'Apply'.
|
|
How can I check to see if a database is available before I send it a
request? |
| Sending AbtDbmSystem activeDatabaseMgr will do the job. If you get
nil back then you are not connected. |
|
Why can't I delete rows using the ODBC text driver? |
| The ODBC text driver supplied with VisualAge 3.0 does not support deletes
or updates. Additional info can be found in the 'VisualAge OBDC Support Drivers
Reference'. |
|
How do I find out what a SQL error message means? |
| Try looking in the VisualAge for Smalltalk online Features Class Guide and
Reference in section 1.4.4 titled Error Detection and other tips. |
|
Can I use stored procedures? |
| Version 3.0 now supports Stored Procedures with our ODBC feature and our
Native Oracle feature. If you are connecting to Sybase through ODBC, then you
should be able to use stored procedures. This information and more is available
in the VisualAge for Smalltalk User's Guide on page 205 Using stored procedures. |
|
Why do I get the error "Undefined object does not understand contents"? |
| Try changing the "widget notNil" test in
AbtTextViewFormatManager>>userInputString to "self isWidgetUsable". |
|
How do I convert my queries to another database? |
A tool is provided in VisualAge Version 3 which helps users migrate their
Version 2 database parts to Version3. This tool also helps users to migrate
their query parts to use different connection specifications. See p.429 of the
VisualAge User's Guide for additional information about this tool. The general
steps for migrating your query parts (for cases a and b) would be as follows:
1) Modify an existing connection specification for your application
(or create a new specification) so that it contains information about the
desired (target) database connection
2) Follow instructions on p.
429 to execute the migration tool for the parts that require migration
Migration
will be possible if the table names and column names for your target database
connection match those for your original connection. |
|
Is there an ability for the end user application to cancel a database call? |
Native Oracle support contains an API called 'break' which will
asynchronously terminate any long running operations for a database connection.
This method can be executed as follows:
(AbtDbmSystem activeDatabaseConnectionWithAlias: 'Oracle' ) break
ODBC and IBM database support do not currently implement any similar
functionality. In answer to your question regarding threads, threaded database
calls are executed with a 'threadKey' equivalent to theAbtDatabaseConnection
instance that executes the DB call. Therefore, a thread could be terminated by
executing the following code:
AbtThreadManager terminateThread:
(AbtDbmSystem activeDatabaseConnectionWithAlias: 'x').
|
|
Does VA support multiple database connections per process? |
In Version 3, multiple database connections are permissable. VisualAge
manages these multiple connections by retaining connection 'aliases' which map
to actual connections.
Below is an example of the recommended V3
approach for establishing a database connection via Smalltalk code. (Notice
that the recommended steps forestablishing a database connection have changed.
The old technique for connecting is still supported, but is slightly less
flexible )
| dbSpec1 dbConnection1 |
dbSpec1 := AbtDatabaseConnectionSpec
forDbmClass: AbtOdbcDatabaseManager
dataSourceName: 'Local'.
" activate the connection described by dbSpec1 passing in required
logon information "
dbConnection1 :=
dbSpec1 connectUsingAlias: 'Local'
logonSpec: ( AbtDatabaseLogonSpec new id: 'USERID' ;
password: 'PASSWORD' ;
server: 'Local' ;
yourself ).
The approach above is useful if you are using
Smalltalk code to connect. However, the VisualAge visual database parts are
designed to prompt for logon information each time a new connection is
established. There is a simple way to override this behavior.
A
programmer can 'register' logon information which remains active for as long as
the image is active ( the information is cleared when the image is re-started).
ie)
AbtDbmSystem registerLogonSpec:
logonSpec: ( AbtDatabaseLogonSpec new id: 'USERID' ;
password: 'PASSWORD' ;
server: 'Local' ;
yourself ) withAlias: 'Local'.
After the above statement is
executed, the supplied logon spec will be used any time you attempt to activate
the connection with alias 'Local'. The #removeLogonSpecWithAlias: can
be used to undo the above action. |
|
What should I do if I'm having packaging and runtime problems with DB2? |
VisualAge V3 stores each individual query as a separate method within your
access set.
The runtime packager algorithm is designed to eliminate
unreferenced selectors from your packaged image. I suspect that you are setting
your querySpecName: to a String containing the name of a query specification.
The packager does not recognize Strings as selector names; therefore, query
names set using a String will not be included in the packaged image unless
referenced elsewhere by your application. However, if you set your
querySpecName using a hardcoded Symbol, the packager WILL include the runtime
selector for your query.
You have at least 2 options for correcting
this problem...
1) Change all references to query spec names from Strings
to Symbols.
ie) dbPart querySpecName: 'MyQuery'
- changed to -
dbPart querySpecName: #MyQuery
-OR-
2)
Implement a method called #packagerIncludeSelectors in your
accessSetClass.
This method answers an Array containing the names of
selectors that you wish to include in the package image. This method is only
necessary for cases where you wish to include a selector which is not directly
referenced by the application.
Example - To package runtime selectors
for all querySpecs contained within MyAccessSet, I would create a class method
called #packagerIncludeSelectors in class MyAccessSet. The code would
look like :
packagerIncludeSelectors
( self registeredQuerySpecNames
collect: [:specName ] specName asSymbol ] ) asArray
To force queries 'Abc' and 'Def' to be packaged, the #packagerIncludeSelectors
method would look like:
packagerIncludeSelectors
#( Abc Def )
There is additional packaging information on p333 of the IBM ST
User's Guide. |
|
Can VA be used to generate non-ANSI SQL? |
| The VA SQL Editor was built based on ANSI SQL and cannot be used to build
non-ANSI SQL. Yes, one can be created manually. We know of no limitations in
allowable syntax for SQL statements. In some cases, it may be possible for you
to build your initial 'ANSI' query using the SQL Editor, then manually edit the
query to add any 'non-ANSI' functionality. VA merely passes your query string
to the database connection. No syntax validation is done within VA itself. |
|
What do I have to do to provide a BLOB object to a column of the currentRow? |
| The SQL statements generated by an APPLY upon a updated query result table
includes the values as litterals (which is obviously difficult for a BLOB).
INSERT or UPDATE SQL statements created by an SqlStatement part can include
values as hostvariables. Using this way, I'm able to insert BLOB in the
database. |
|
What should I do if I cannot retrieve a BLOB using DB2? |
When VisualAge retrieves a BLOB from DB2/2, it does not have a concept of
the class that was used to store the data. If you would like to create a new
instance of your OSObject subclass using the ByteArray from your retrieved BLOB,
you can do so as follows:
MyOSObjectSubclass reference: theBlobByteArray
OSObjects contain an instance variable called reference
which can contain a ByteArray or an address to OSMemory. The code above
instantiates the OSObject subclass and sets the 'reference' to the BLOB
ByteArray. |
|
How do we prevent the error prompter from being displayed? |
Each query part has its own #errorBlock attribute which can be
individually set prior to query execution. The query parts circumvent the
default error block set in the active database manager instance by passing in an
errorBlock when executing database API calls. Prior to executing a query, you
can set its errorBlock in a script. ie)
(self subpartNamed: 'Multiple Row Query1') errorBlock: [ your BLOCK ].
Or, you can create a VisualAge event-to-script connection to a
method which returns the errorBlock and connect the 'result' of the connection
to the #errorBlock attribute of your query part. |
|
Where can I get information about CLI? |
The IBM CLI Database feature is a reimplementation of the IBM Database
Manager, bringing our database manager count to four:
1. IBM Database
2 - "original"
2. IBM Database 2 - CLI
3. ODBC
4.
Oracle - Native
Our original DB2 support used a DLL that we
provided. That DLL used embedded SQL. It had some shortcomings. It didn't
support multiple connections, and it didn't handle concurrent applications well.
It needed to be ported to Windows 95 and Windows NT. Furthermore, it is not
possible to support multiple concurrent connections using embedded SQL (you can
have multiple connections, but only one active connection). Faced with these
problems, we decided it was time to change interfaces.
DB2 provides
a second dynamic interface, the Call Level Interface (CLI). This interface
supports multiple concurrent connections. The CLI DLL is shipped with each
DB2/2 client, so our customers already have it. It's designed for concurrency
of applications. It supports distributed unit of work (multiple connections, one
transaction). It's available on all platforms. So,... we now support the CLI.
The CLI should have the same public interface as the original DB2
support, so migration is easy. It is necessary to use
AbtEditDatabaseMigrationApp to migrate any of the visual database query parts,
however. (This was documented in V3.0, you load the app and execute
AbtDatabaseMigrationView new openWidget).
The CLI feature is
available on all platforms (the original DB2 support has not been ported to 95
or NT), and it is the implementation that we will be using in the future. The
original DB2 support will eventually be dropped. |
|
Why do I get an error of "Connection limit reached"? |
From the db2 command line processor enter 'query client'. Take a look at
the value for 'MAX_NETBIOS_CONNECTIONS', if this is 1 then use the 'set client'
command to increase this value. I'm assuming you're using netbios for
communications, if you're not then repost with the sql error number you're
receiving.
To prevent the logon prompt for the aliases that you have as
prompt no, register a logon spec for each one.
AbtDbmSystem registerLogonSpec: (AbtDatabaseLogonSpec new
id: 'userid'; password: 'password'; server: 'sample')
withAlias: 'VAIBMSamples'
|
|
Why are we having problems with our VA ODBC drivers? |
I have been able to get the VisualAge odbc.dll driver manager to work with
the db2 odbc driver (db2cli.dll). I did not use the db2 'odbc installer' to
install any drivers. Here are the steps I followed:
1. Catalog your
database(s)
2. Start the 'CLI-ODBC Administrator' program. From here you
can select the database alias and configure the database you want to access via
the visualAge odbc feature.
3. From VisualAge you should now be able to
create a connection alias using the data source you just configured. |
|
How can I define my script to only read 50 rows? |
Try using #for:do:ifError: instead of #do:. the first
argument is the number of rows you want, you mentioned 50. Alternatively, you
could do something like
50 timesRepeat: [
aRow := rows next.
..... ].
|
|
What is the function of the addRows: method of AbtTableClass? |
The #addRows: message can be used for ODBC, IBM CLI, or Native
Oracle to add a collection of rows to a database table with one API call. The
#addRows: message can be significantly faster for some cases because
multiple data rows are added with only one trip to the database server.
The
parameter name 'aRowSet' is a bit deceptive. 'aRowSet' should be a collection
of AbtRow objects. In fact, 'Set' objects cannot be used for this API. |
|
Is there a way to set the isolation level of a DB2 database connection? |
Yes, there are two ways. One way is to change your db2cli.ini file to
include 'TXNISOLATION = 1'. This will make all connections to the database use
this isolation level by default. The isolation levels are:
1 = Read
Uncommitted (Uncommitted read)
2 = Read Committed (Cursor stability)
(default)
8 = Serializable (Repeatable read)
16= Repeatable Read
(Read Stability)
32= (No Commit, DATABASE 2 for OS/400 only) The words
in round brackets are the DB2 equivalents for SQL92 isolation levels."
(This is from DB2 Call Level Interface Guide and Reference.)
The other
way is to use the set connection option api. VisualAge has a method, #setConnectOption:withHdbc:value:ifError:,
that calls this api. For example,
myConnection
setConnectOption: "Sql_Txn_Isolation" 72
withHdbc: self hdbc
value: "Sql_Txn_Read_Uncommitted" 1
ifError: self errorBlock.
|
|
Where can I find a list of all values for the constants? |
| I find them by looking in the C include files, sqlcli.h and sqlcli1.h. They
are found in your sqllib\include directory if you have the Software Developers
Kit for DB2. |
|
What licenses are needed for VAST developers accessing a DB2 server? |
| Each VisualAge client image needs a connection to the DB, *if* the design
has each directly using the DB. DB2/2 restrictions, if any, are per DB2's
design for handling multiple users simultaneously. This is business as usual
for DB2. You can also design your client-server app so that only the server app
or only some client-side functions need DB access. |
|
Do I have to follow a stored procedure execution with a commit? |
| There is an auto-commit option that you may like. If you send #autoCommit:
true to your connection instance, commits will be done for you.
|
|
Why would I set the AbtDatabasePart's "database" attribute to nil? |
As the comment states, the intention of setting the 'database' attribute to
nil is to "Clear the database connection to force re-validation of
settings".
Prior to executing a query, the current algorithm used
by database query parts to validate settings will only execute if the 'database'
attribute is nil. For typical usages of the query parts, settings
validation only occurs the first time the part is executed in order to validate
the pre-saved settings. Subsequent query executions would occur without need to
validate the part settings. The change that is causing you 'grief' was
implemented to prevent walkbacks that occured when an application set the
querySpecName to an invalid name, then attempted to execute the query. Setting
the 'database' attribute to nil caused the setting validation routine to
re-execute and report an error rather than causing a walkback. For your case,
there seems to be an undesired side-effect.
Potential solution...
Setting
the cached 'database' attribute to nil clears the database connection for the
part, but the database connection is still active within the image. When
setting the value of the 'database' attribute, VisualAge looks for an active
database connection with an 'alias' that matches the connectionAlias for the
part. The logon prompt will NOT appear if the connection 'alias' of an active
database connection matches the current 'connectionAlias' setting for the
database part. In this case, the 'database' attribute for the part is set to
the existing database connection instance.
FYI. If the connectionAlias
is not supplied on connect, the default is 'DatabaseManagerClass_DatabaseName'.
Verify that the connectionAlias for your part matches the desired active
database connection.
Alternatively, you can comment out the 'self
database: nil' from the VisualAge code to restore the V3.0 behavior. We
will look for an alternative approach which does not cause the side effect that
you've discovered. |
|
How can I integrate a DB from VA with a DB in Lotus server? |
You change the database design:
When you first establish your Notes
Database in VisualAge, and in particular when you select the alias for the part,
VisualAge takes a "snapshot" of the database to keep track of what the
selected view or form looks like in Notes (depending on what VA part we're
discussing. As you discovered, if the Notes database subsequently changes this
snapshot and the database are out of sync.
You can remedy this by
taking the following steps:
1. delete any quick forms related to the
part.
2. open the settings for the form or view part and reselect the
alias. This creates a new snapshot of the database.
3. recreate any
quickforms you had.
Note that this is no different than the
relational database parts. If the design of the relational database changes you
may need to take these same steps with regard to your VA relational db parts.
- You change the contents of the database:
Although you're
generally unaware of this, this is exactly how Notes works. Each client has
their own view of the database and the documents in it. When you select refresh
in the client (or when you reopen the datase) this view is reconstructed and
changes that other users made to the database now become visible to you. The
way you update this view in VA is to trigger the update action on the view. I
generally do this by connecting a Refresh menu item's clicked event to the
update action. Unlike the notes client, we do not automatically update a view
when you open the database for performance reasons. So, if you want the view
automatically refreshed when you open the database you will need to trigger the
update action there as well. This is discussed in section 8.7.1.2.1.1 of the
online documentation (search on update). |
